Carrier for a fastening element to be fabricated and a method for production thereof, particularly as an orthodontic bracket

ABSTRACT

A carrier for at least one fastening element ( 4 ) to be fabricated having an attachment area whereby the carrier is provided with a holding piece ( 3 ) for attachment in a receiving part of a finishing machine and whereby the carrier includes a carrier piece ( 2 ) for the fastening element ( 4 ) and the carrier piece ( 2 ) is embedded at least partially in the carrier piece ( 2 ) in a manner so that the attachment area ( 4   b ) of the fastening element ( 4 ) can be fabricated. A method for producing a fastening element ( 4 ) to be finished and to be attached to an individual surface whereby the contour of the attachment area is defined with the aid of data of the surface onto which the fastening element ( 4 ) is to be attached and whereby a pre-shaped, not yet individualized fastening element ( 4 ) is formed by removal of material to produce the specific contour. Furthermore, an auxiliary positioning part ( 21 ) is provided with a contour that is continued by the contour of the attachment area, which is also defined by the surface onto which the fastening element ( 4 ) is to be attached.

CROSS-REFERENCE RELATED APPLICATION

This application is related to U.S. Provisional Application No. 60/755,085, filed Jan. 3, 2006, the priority of which is hereby claimed, and it claims priority of German Patent Application No. 10 2005 025 5574, filed Jun. 1, 2005.

FIELD OF THE INVENTION

The invention relates to a carrier for a fastening element to be fabricated, a fastening element and a method for the production of this fastening element, particularly as an orthodontic bracket.

The PRIOR ART

DE 693 27 661 T2 discloses the production of an orthodontic bracket whereby a slot for an arch wire is cut into a bracket blank. Cutting of the slot is performed according to individual requirements after a corresponding computation by means of a program. A holding piece constructed individually for each tooth is fabricated for the individually constructed bracket made from round plastic disks. The radius of the cutter of the fabricating tool is thereby taken into consideration.

It is of disadvantage in this case that the individual conditions of the attachment area on the tooth are not taken into consideration even with the individual design of the slot and the holding piece. This has the result that adjustment to the individual conditions is achieved totally through the amount of adhesive material or cement and this material has to transfer holding forces through different thicknesses.

Attention has to be paid additionally that the specific assignment of individual holding pieces and of individual brackets does not get lost, thus requiring great care during transport or during the subsequent installation.

U.S. Pat. No. 4,284,405 discloses a device and a method for orthodontic care wherein a model of the tooth situation is created and whereby a plate-like fixture is formed for positioning of the orthodontic appliance.

US 2004/0219473 discloses an orthodontic device which is positioned on the tooth with the aid of a replica of the tooth surface. The replica is produced with the aid of a teeth impression.

US 2003/0194677 A1 discloses a method and a device for the production of an orthodontic template assisting in the positioning of an orthodontic device. The template is designed with the aid of a computer based on the data set of the patient's tooth situation and it is manufactured by means of grinding, three-dimensional pressing and/or molding from a molten mass.

The disadvantage of the aforementioned orthodontic methods and devices is the fact that the orthodontic fastening devices have a standard geometry which cannot be adjusted to the geometry of the tooth surface. In addition, a great number of working steps are necessary for the realization of the methods mentioned above.

Based on the known methods and devices there is created the desire for a simple, cost-effective and realizable solution to produce orthodontic devices which can be accurately positioned and which can be manufactured based on a CAD/CAM processing plan with traditional commercial and proven automatic grinding/finishing machines.

SUMMARY OF THE INVENTION

The carrier according to the invention is provided with a holding piece for fastening in the receiving part of a finishing machine whereby the carrier comprises a carrier piece for the fastening element. The fastening element or bracket is at least partially embedded in the carrier piece in a manner so that the attachment area of the fastening element can be fabricated. A carrier can be clamped into a finishing machine and shaped therein and the attachment area of the fastening element can be individualized thereby.

The fastening element is advantageously a bracket used in the field of dental orthopedics with a pre-manufactured holding part at the front or with a holding part to be formed for an additional attachable component and an attachment area at its rear side for fastening to a tooth.

The fastening element is advantageously connected to the carrier piece at a lateral region between its front and rear side. This makes possible easy accessibility of the tools of the finishing machine to the fastening element.

The connection is advantageously designed as a connection with positive fit whereby especially a snap connection is preferred. Such a snap connection of a suitable design can be disconnected easily.

At least two fastening elements are provided on the carrier at a distance apart. The number of fastening elements to be finished by the respective finishing machines is usually considerably greater compared to finishing large-sized fastening elements so that the efficient production of several brackets is made possible in one working step, especially if the fastening elements are orthodontic brackets. As a rule, a large number of brackets are required at the same time in orthodontic care. The attachment of several fastening devices on one carrier is therefore highly economical.

The fastening elements are advantageously arranged along a longitudinal axis of the carrier piece. This makes fabrication in the finishing machine easier.

The carrier piece is advantageously provided with two sections arranged about the longitudinal axis. It is made possible thereby to double the number of fastening devices to be fabricated in one working step by having nearly the same space requirements as a one-sided carrier piece.

At least two sections are preferably connected to one another by the same material and they are preferably aligned to one another at an angle of 75 degrees to 90 degrees. Both sections are then highly accessible for the finishing machine.

It is especially advantageous if the fastening elements are arranged on the sections along the longitudinal axis in an offset manner. This makes a quicker finishing process possible.

The attachment area of the fastening element is advantageously totally embedded into the carrier piece. A carrier of this type can be produced in an especially cost-effective way.

The fastening element advantageously projects past the carrier piece with a holding piece for a tensioning element. This makes easier subsequent gripping and positioning of the holding piece on the tooth surface.

The material of the fastening element and the material of the carrier part is different so that an adhesive used for attachment of the fastening element to the tooth adheres only to the fastening element itself. The carrier piece is thereby prevented from being also glued to the tooth whereby especially easy manipulation of the carrier piece is achieved relative to the fastening element.

The fastening element is made of metal and the carrier piece is made of a polymeric material in an especially advantageous embodiment. A metal fastening element has sufficient stability for employment in orthodontic care and it is bio-compatible with the appropriate choice of material.

As an alternative it is possible to make the fastening element of a ceramic. Ceramic has especially good aesthetic characteristics since it is possible to adjust the color of the ceramic to the color of the tooth.

The carrier piece advantageously made of PTFE (polytetrafluoroethylene). PTFE, which is often called Teflon, can be processed well in finishing machines and does not adhere to many adhesives.

The holding part of the fastening element can also advantageously be shaped in a manner to influence the direction of action for the additional component to be attached. This makes possible the employment of straight, non-deformed wires (straight wire technology) whereby the bending of wires for the defined creation of forces upon individual teeth is no longer necessary or it is greatly simplified.

A predetermined breaking point is advantageously provided in the carrier piece adjacent to the attachment area of the fastening element. This makes the removal of the carrier piece easier during attachment of the fastening element to the tooth.

The carrier piece is advantageously manufactured using injection molding technology and the fastening element is embedded into the carrier piece as an inserted part. Such a carrier piece can be manufactured in a highly cost-effective manner.

It is especially of advantage if at least fourteen fastening elements are provided on the carrier whereby the fastening elements are preferably designed differently from one another. At least fourteen fastening elements are usually required for each jaw in orthodontic care. Specific requirements are placed on the fastening elements depending on the location of employment which are reflected in the different design of the fastening elements.

An additional object of the invention relates to a fastening element having an attachment area whereby this attachment area is surrounded with an auxiliary positioning part. The attachment area and the auxiliary positioning part are individually shaped in a finished condition and they have, at least sectional, the shape of the surface onto which the fastening element is to be attached. Such an individually fabricated fastening element can be shaped in a manner so that it is possible to attach the fastening element onto the tooth with its attachment area by means of a uniformly thick adhesive layer, on the one hand, and to be able to vary the spatial orientation of the fastening element in many parameters, on the other hand (orientation of the front holding device, distance of the front holding device between the tooth, etc.)

The attachment area is advantageously covered by the auxiliary positioning part in an unfinished condition. It is made possible thereby to shape the auxiliary positioning part according to the natural arch of the tooth.

The attachment area of the fastening element is not covered by the auxiliary positioning part in the finished condition. This makes attachment of the fastening element to the tooth surface possible.

The auxiliary positioning part is advantageously provided with a predetermined breaking point. The auxiliary positioning part can thereby be easily removed from the tooth after positioning of the fastening element.

It is alternatively possible to attach the auxiliary positioning part to the fastening element by means of a detachable connecting piece. Advantageously, the detachable connection can be a snap connection.

It is of special advantage if the attachment area is set back relative to the auxiliary positioning part by an offset from the surface onto which the fastening element is to be attached. This allows enough space for application of a suitable adhesive whereby the set-back is chosen to correspond to the desired thickness of the adhesive.

In a method to produce a fastening element to be finished and to be attached to an individual surface, particularly in the field of dental orthopedics as an orthodontic bracket, the contour of the attachment area is defined with the aid of data of the surface onto which the fastening element is to be attached whereby a pre-shaped, not yet individualized fastening element is formed by removal of material to produce the specific contour. In addition, an auxiliary positioning part is provided with a contour that is continued by the contour of the attachment area and which is also defined by the surface onto which the fastening element is to be attached.

This fabrication can be achieved especially in a grinding machine suitable for finishing dental ceramic.

The fasting element is advantageously provided with a not yet individualized holding piece for a component to be held in place, whereby the holding piece is disposed on the side facing away from the attachment area and whereby the holding piece is shaped to conform to the individual surface of the component to be held with consideration of the orientation of the component. It is made possible thereby to design the fastening element in a manner so that a straight wire can be used. The determination of the amount of forces to be applied to the individual tooth is achieved through the position and orientation of the fastening element and of the holding piece on the tooth.

The attachment area of the fastening element is set back relative to the contour of the auxiliary positioning part by an offset from the surface onto which the fastening element is to be attached. A gap for the adhesive is created thereby which can be filled with a thick adhesive layer, depending on the distance of the offset, whereby the fastening element can be positioned and attached to the tooth with a very high accuracy in positioning and by having an adhesive layer of defined thickness.

The invention will now be better understood by reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. I shows a carrier with a plurality of fastening elements in the form of brackets;

FIG. 2 shows a partial sectional view along line 2-2 of FIG. 1;

FIG. 3 shows a sectional view along line 3-3 of FIG. 2;

FIG. 4 shows a perspective view of the carrier together with a fabrication tool;

FIG. 5 shows a row of teeth with several glued-on brackets together with auxiliary positioning parts;

FIG. 6 shows a cross-sectional view along line 6-6 of FIG. 5 of a bracket with an auxiliary positioning part on a tooth;

FIG. 6 a shows in detail a snap connection of the auxiliary positioning part on the bracket;

FIG. 7 shows the bracket together with the auxiliary positioning part from FIG. 6 without the tooth;

FIG. 8 shows the row of teeth from FIG. 5 after removal of the auxiliary positioning part and after the attachment of a tensioning wire;

FIG. 9 shows the arrangement of the brackets and the auxiliary positioning parts from FIG. 1;

FIG. 10A shows the fabrication of a bracket to produce a first design of a receiving part for a tensioning element; and

FIG. 10B shows the fabrication of the bracket to produce a second design of a receiving part for a tensioning element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a carrier 1 comprising a carrier piece 2 and a holding part 3 for attachment to a non-illustrated receiving part of a finishing machine. A plurality of fastening elements 4 are arranged in the carrier piece 2. The fastening elements 4 are juxtaposed along a longitudinal axis 5 of the carrier.

FIG. 2 shows a sectional view along line 2-2 in FIG. 1. Portions of the fastening elements 4 project past the carrier piece 2. It can be clearly seen in conjunction with FIG. 3 that the carrier piece 2 consists of two sections 2 a and 2 b which are one piece and which form an angle of approximately 90 degrees. Section 2 a and section 2 b are accessible from the rear, which means the side facing the longitudinal axis 5, for finishing with a fabrication tool.

It can be seen furthermore that one side of each fastening element 4 facing away from the carrier piece 2 is provided with a holding piece 4 a whereby the opposite side, which is an attachment area 4 b, is completely embedded in the carrier piece 2.

The holding piece 4 a of the fastening element 4 is already provided with a slot 4 c to receive a tensioning element (not illustrated). The slot 4 c is either contained in the still unfinished carrier 1 or it is individually fabricated in a finishing process of the carrier 1 by means of a suitable fabrication tool with a fixed setting corresponding to the fastening elements.

FIG. 4 shows in a perspective view the carrier 1 from FIG. 1 through FIG. 3. In addition, there is shown the pin-shaped fabrication tool 6 in the form of a grinder or cutter which can be moved in a relative movement corresponding to the spatial axes of the carrier 1 as illustrated by arrows. The inner side of the section 2 a can be worked on in the shown position of the carrier 1 to produce a predetermined contour. The carrier piece 2 is finished in the region of the attachment area 4 b during the material-removing process to such a degree that the attachment area is completely laid open and is no longer covered by the material of the carrier piece 2. The area of the carrier piece 2 adjacent to the attachment area 4 b is also finished whereby the contour of the attachment area is continued.

Nevertheless, it is possible to produce a separate auxiliary positioning part based on the existing surface data and to attach this auxiliary positioning part at a later time on the fastening element preventing simultaneous production, on the one hand, and faulty arrangement of the positioning part to fastening part, on the other hand.

FIG. 5 shows a row of teeth 20 made up of the teeth 20 a through 20 d whereby the bracket 4 is attached to the teeth together with the surrounding part of the former carrier piece 2 designed as an auxiliary positioning part 21. It can be seen that the auxiliary positioning part are on tooth 20 a is oriented approximately axis-parallel to the fastening element 4, whereas the auxiliary positioning part 21 b on tooth 20 b is rotated clockwise relative to the fastening element 4. An auxiliary positioning part 21 c on tooth 20 c is rotated in an opposite direction compared to the one on tooth 20 b and the auxiliary positioning part 21 d on tooth 20 d is again oriented approximately axis-parallel.

Even though the fastening elements in the carrier are all oriented the same according to FIG. 1, an auxiliary positioning part can be provided through specific fabrication leading to a slanted position of the fastening element relative to the other fastening element. It is required thereby that the number of fastening elements in FIG. 1 have sufficiently large spaces between each other on the carrier piece 2.

FIG. 6 shows a sectional view along line 6-6 in FIG. 5. A fastening element 4 is attached to tooth 20 a either with adhesive or cement. The orientation of the fastening element 4 on tooth 20 a is achieved by means of the auxiliary positioning part 21 a which is connected in turn to the fastening element 4 with a snap connection 23. Care has to be taken during attachment of the fastening element 4 to tooth 20 a so that the auxiliary positioning part 21 a itself is not bonded to tooth 20 a. The adhesives or the types of cement used to attach the fastening element 4 will not bond with the auxiliary positioning part itself if the auxiliary positioning part is made of a material such as PTFE, for example.

The snap connection 23 is illustrated in FIG. 6 a and it can be seen that the auxiliary positioning part 21 a is provided with a snap-on projection engaging the cutout on the fastening element 4. In addition, this cutout is additionally helpful during removal of the bonded fastening element 4 from tooth 20 a.

The auxiliary positioning parts 21 a through 21 d are provided with predetermined breaking points 22 a through 22 d for easier removal of the positioning parts after attachment 4 a through 4 d to the teeth 20 a through 20 d.

Even though there is not shown in FIG. 6 a receiving slot 4 c with an axis-parallel orientation, the slot can still extend in another direction as it is already known and required in the production of brackets to pull the tooth 20 a down-ward or to lift it up, for instance.

FIG. 7 reflects the position of the attachment area 4 b of the fastening element 4 whereby the contour of the attachment area 4 b conforms to the predetermined surface of tooth 20 a, possibly with consideration of a correction value for the bonding material, particularly adhesive or cement. The positioning area of the auxiliary positioning part 21 laterally abuts the attachment area 4 b whereby the contour of the auxiliary positioning part conforms to the surface of tooth 20. A gap measurement is not required to be taken into consideration here since no bonding material is used such as an adhesive or cement.

The position of an adhesive layer 24 is shown in FIG. 6 a. It can be additionally advantageous to provide compensation spaces in the auxiliary positioning part 21 a to receive excess bonding material such as adhesive or cement (not illustrated).

FIG. 8 illustrates the row of teeth 20 from FIG. 5 after a tensioning element 30 has been inserted into the fastening elements 4 and after the auxiliary positioning part 21 has been removed.

The tensioning element 30 is a straight wire with defined elasticity, which is tensioned in a bent shape through the position and orientation of the fastening elements 4, 4′, 4″, 4′″ on the teeth 20 a through 20 d and the position of the holding pieces 4 c. The tensioning element 30 exerts a defined translatory and/or rotatory force on each of the teeth 20 a through 20 d through its elasticity corresponding to its curvature whereby the force leads to the desired displacement of the respective teeth 20 a through 20 d.

Removal of the auxiliary positioning part is easily possible after bonding of the fastening element 4 since is consists of a non-adhesive material, e.g., Teflon, and it can be simply taken off by means of the snap connected and/or the predetermined breaking point. Only the accurately positioned fastening element 4 remains now on the tooth.

The positioning of the fastening element 4 on the tooth 20 a with its connected auxiliary part 21 is achieved in that a position is searched by moving the fastening element along tooth 20 whereby the largest coverage of the outer surface of tooth 20 is made with the inner surface of the fastening element 4 or of the auxiliary positioning part 21. A firm connection is created through pressing of the fastening element 4 against the tooth 20, possibly under the simultaneous influence of heat and/or light.

Displacement by sliding of the fastening element and its connected auxiliary positioning part 21 is prevented in that a much greater contact surface exists between tooth 20 and the auxiliary positioning part 21 after reaching the fitting position than before so that a considerably greater force would be necessary to push the auxiliary positioning part 21.

The fastening element 4 can be moved to a small degree relative to the surrounding auxiliary positioning part 21 in that the attachment area 4 b of the fastening element 4 is set back relative to the positioning area of the auxiliary positioning part 21 whereby the snap connection allows a certain tolerance of movement toward the attachment area 4 b. The fastening element 4 is thereby guided along the sides of the surrounding positioning part 21.

It is achieved thereby that a small gap is developed between the fastening element 4 and the extension of the surface of the auxiliary positioning part 21 whereby the gap is filled with an adhesive and a uniformly thick adhesive layer is created thereby.

Forces developed during fabrication are easily absorbed during manufacturing of the recess 4 c in that the fastening element 4 is completely embedded in the carrier piece at the side of the attachment area 4 b. Shaping of the attachment area 4 b and fabrication of the auxiliary positioning part, which is formed from the carrier piece 2, occurs only after the fabrication of the receiving part 4 c.

FIG. 9 illustrates how the auxiliary positioning parts 21 a through 21 d from FIG. 5 can be produced from the carrier part shown in FIG. 1.

FIG. 10 illustrates how a recess 4 c is produced in the fastening element 4 extending straight across or at an angle. This can be achieved through rotating of the carrier 1 about its longitudinal axis 5 corresponding to FIG. 4 and this longitudinal axis must be in place should there be proposed more than one carrier section provided with fastening elements so that the fabrication tool 6 can reach the attachment areas of the fastening elements.

As an alternative to the placement of the fastening element 4 relative to the auxiliary positioning part 21 illustrated in FIG. 9, which is essentially defined by the direction of the recess 4 c, it is also conceivable to place the auxiliary positioning part 21 and the fastening element 4 always parallel to one another and to give the recess also the desired direction along the directional axis 5 through corresponding fabrication. 

1. A carrier for at least one fastening element (4) to be fabricated having an attachment area, such as an orthodontic bracket, whereby the carrier is provided with a holding piece (3) for attachment in a receiving part of a finishing machine and whereby the carrier comprises a carrier piece (2) for the fastening element (4), wherein the carrier piece (2) is embedded at least partially in the carrier piece (2) in a manner so that the attachment area (4 b) of the fastening element (4) can be fabricated.
 2. A carrier according to claim 1, wherein the fastening element (4) is a bracket used in the field of dental orthopedics with an already manufactured holding part at the front or with a holding part to be formed for an additional attachable component (30) and an attachment area (4 b) at its rear side for fastening to a tooth (20).
 3. A carrier according to claim 1, wherein the fastening element (4) is connected to the carrier piece (2) at a lateral region between its front and rear side.
 4. A carrier according to claim 3, wherein the connection is a snap-on connection.
 5. A carrier according to claim 1, wherein at least two fastening elements (4) are provided in the carrier (1) such that said fastening elements are disposed at a distance apart from one another.
 6. A carrier according to claim 5, wherein the fastening elements (4) are arranged along a longitudinal axis (5) of the carrier piece (2).
 7. A carrier according to claim 6, wherein the carrier piece (2) is provided with at least two sections (2 a, 2 b) arranged about the longitudinal axis (5).
 8. A carrier according to claim 7, wherein the sections (2 a, 2 b) are one piece and form an angle of 75 degrees to 90 degrees.
 9. A carrier according to claim 7, wherein the fastening elements (4) are arranged offset to one another on the sections (2 a, 2 b) along a longitudinal axis (5).
 10. A carrier according to claim 1, wherein the attachment area (4 b) of the fastening element (4) is totally embedded (2) in the carrier piece (2).
 11. A carrier according to claim 10, wherein the fastening element (4) projects beyond the carrier piece (2) with a holding piece (4 a) for a tensioning element.
 12. A carrier according to claim 1, wherein the material of the fastening element (4) and the material of the carrier part (2) are different so that an adhesive used for attachment of the fastening element (4) to the tooth (20) adheres only to the fastening element (4) itself.
 13. A carrier according to claim 12, wherein the fastening part (4) is made of metal and wherein the carrier part is made of a polymeric material.
 14. A carrier according to claim 12, wherein the fastening part (4) is made of ceramic and wherein the carrier part is made of a polymeric material.
 15. A carrier according to claim 12, wherein said carrier piece consists of PTFE (polytetrafluoroethylene).
 16. A carrier according to claim 10, wherein the holding piece (4 a) of the fastening element (4) can also be shaped in a manner to influence the direction of action for the additional component to be attached.
 17. A carrier according to claim 1, wherein a predetermined breaking point (22) is provided in the carrier piece (2) adjacent to the attachment area (4 b) of the fastening element (4).
 18. A carrier according to claim 1, wherein the carrier piece (2) is injection molded and the fastening element (4) is embedded into the carrier piece as an inserted part.
 19. A carrier according to claim 1, wherein at least fourteen fastening elements (4) are provided on the carrier and said fastening elements are designed differently from one another.
 20. A fastening element having an attachment area (4 b), such as an orthodontic bracket used in the field of dental orthopedics, wherein the attachment area (4 b) is surrounded with an auxiliary positioning part (21) whereby the attachment area (4 b) and the auxiliary positioning part (21) are individually shaped in a finished condition and they have at least at one matching section of the surface onto which the fastening element (4) is to be attached.
 21. A fastening element according to claim 20, wherein the auxiliary positioning part (21) covers the attachment area (4 b) of the fastening element (4) in an unfinished condition.
 22. A fastening element according to claim 20, wherein the attachment area (4 b) is not covered by the auxiliary positioning part (21) in a finished condition.
 23. A fastening element according to claim 20, wherein the auxiliary positioning part (21) is provided with a predetermined breaking point (22).
 24. A fastening element according to claim 20, wherein the auxiliary positioning part (21) is secured to the fastening element (4) by means of a detachable connection.
 25. A fastening element according to claim 24, wherein the detachable connection is a snap-on connection (23).
 26. A fastening element according to claim 20, wherein the attachment area (4 b) is set back relative to the auxiliary positioning part (21) by an offset (t) from the surface onto which the fastening element is to be attached.
 27. A method for producing a fastening element (4) to be finished and to be attached to an individual surface, such as in the field of dental orthopedics as an orthodontic bracket attached to a tooth, wherein the contour of the attachment area (4 b) is defined with the aid of data of the surface onto which the fastening element (4) is to be attached whereby a pre-shaped, not yet individualized fastening element (4) is formed by removal of material to produce the specific contour whereby additionally an auxiliary positioning part (21) is provided with a contour that is continued by the contour of the attachment area (4 b), which is also defined by the surface onto which the fastening element (4) is to be attached.
 28. A method according to claim 27, whereby the fasting element (4) is provided with a not yet individualized holding piece (4 a) for a component to be held in place, whereby said holding piece (4 a) is disposed on the side facing away from the attachment area (4 b), and whereby said holding piece (4 a) is shaped to conform to the individual surface of the component (30) to be held with consideration to the orientation of said component (30).
 29. A method according to claim 27, whereby the attachment area (4 b) of the fastening element (4) is set back relative to the contour of the auxiliary positioning part (21) by an offset (t) from the surface onto which the fastening element is to be attached. 